As shown in FIG. 1, a cellular wireless communication system is mainly composed of a core network (CN for short), a radio access network (RAN for short) and a terminal. The core network is responsible for non-access stratum transactions, such as terminal location update, etc., and is an anchor of a user plane. The access network includes a base station or a base station and a base station controller, and is responsible for access stratum transactions (e.g. management of radio resources). A physical or logical connection may exist between base stations according to the practical conditions, such as a connection among a base station 1, a base station 2 and a base station 3 in FIG. 1, and each base station may be connected to one or more nodes of the core network. A terminal, i.e., a user equipment (UE for short) refers to various devices which may communicate with the cellular wireless communication network, such as mobile phones or notebook computers etc.
The mobility management unit is a unit in the core network which is responsible for managing terminal access control, location information update and handover and is responsible for controlling non-access stratum signaling from the core network to the terminal and registering the terminal to functions of the network, comprising a Mobility Management Entity (MME) or a Serving GPRS Support Node (SGSN).
A Home Subscriber Server (HSS) or a Home Location Register (HLR) is an entity in the core network which is responsible for storing subscription data, identity information, authentication information and authorization information etc. of a terminal device. According to different conditions, the HSS or HLR is available for storing identity information of users and binding information of users and terminal devices, or only storing identity information of users (the binding information of users and terminal devices may be stored by a gateway) or directly storing identity information of terminal devices. The HSS or HLR is also responsible for users' subscription database, and perform authentication and authorization etc. on user identity. A service platform may query user or terminal information from the HSS or HLR.
A Serving Gateway (S-GW) is located in the user plane, and its main function is to perform session management, routing selection and data forwarding, QoS control, accounting, and information storage etc.
A Packet Data Network Gateway (P-GW) is located in the user plane, and its main functions comprise IP address allocation, session management, PCRF selection, routing selection and data forwarding, QoS control, accounting, policy and accounting enforcement etc.
A Machine Type Communication (MTC) InterWorking Function (MTC IWF) is a connection entity between a mobile communication network and an external public network, and can achieve functions such as protocol conversion, address query, and information storage etc. The InterWorking Function may be connected externally to an MTC server, may be connected internally to an HSS/HLR, or may be connected to mobile communication network network elements such as MME/SGSN etc.
An MTC Authentication, Authorization and Accounting (MTC AAA) function entity may retain information of the terminal accessing to the core network and provide authentication and other network services. The MTC AAA may be a RADIUS or Diameter proxy server between the P-GW and the AAA server in an external Packet Data Network (PDN).
Small data transmission refers to that the transmitted data is less than 1024 bits. Bearer resources established by the network for the terminal to transmit and receive data will not be differently treated due to a small amount of data. Therefore, if it only needs to transmit and receive such small amount of data for services of one terminal, the resources allocated by the network will have low utilization.